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Eel
This article is about the elongated fish. For other uses, see Eel (disambiguation). "Eels" redirects here. For the band, see Eels (band). The European conger is the heaviest of all eels. An eel is any ray-finned fish belonging to the order Anguilliformes (/æŋˌɡwɪlɪˈfɔːrmiːz/), which consists of four suborders, 20 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage, and most are predators. The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus), spiny eels (family Mastacembelidae), and deep-sea spiny eels (family Notacanthidae). These other clades, however, evolved their eel-like shapes independently from the true eels. Description: Eels are elongated fish, ranging in length from 5 cm (2.0 in) in the one-jawed eel (Monognathus ahlstromi) to 4 m (13 ft) in the slender giant moray. Adults range in weight from 30 g (1.1 oz) to well over 25 kg (55 lb). They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal fin, forming a single ribbon running along much of the length of the animal. Eels swim by generating body waves which travel the length of their bodies. They can swim backwards by reversing the direction of the wave. Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. A majority of eel species are nocturnal, thus are rarely seen. Sometimes, they are seen living together in holes, or "eel pits". Some species of eels also live in deeper water on the continental shelves and over the slopes deep as 4,000 m (13,000 ft). Only members of the Anguilla regularly inhabit fresh water, but they, too, return to the sea to breed.4 The heaviest true eel is the European conger. The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb). Other eels are longer, but do not weigh as much, such as the slender giant moray which reaches 4 m (13 ft).6 Life-cycle: Main article: Eel life history. Eels begin life as flat and transparent larvae, called leptocephali. Eel larvae drift in the surface waters of the sea, feeding on marine snow, small particles that float in the water. Eel larvae then metamorphose into glass eels and then become elvers before finally seeking out their juvenile and adult habitats. Many eels remain in the sea throughout their lives, but freshwater elvers of eels in the family Anguillidae travel upstream and are forced to climb up obstructions, such as weirs, dam walls, and natural waterfalls. Classification: This classification follows Fish-Base in dividing the eels into 20 families. Additional families included in other classifications (notably ITIS and Systema Naturae 2000) are noted below the family with which they are synonymized in the Fish Base system. Identifying the origin of the freshwater species has been problematic. Genomic studies indicate they are a monophyletic group which originated among the deep-sea eels.8 Suborders and families: A moray eel. Gorgasia barnesi, a species of garden eel. Taxonomy based on Neslon, Grande and Wilson 2016.9 * Suborder Protanguilloidei ** Family Protanguillidae * Suborder Synaphobranchoidei ** Family Synaphobranchidae (cutthroat eels) [incl. Dysommidae, Nettodaridae, and Simenchelyidae]. * Suborder Muraenoidei ** Family Heterenchelyidae (mud eels). ** Family Myrocongridae (thin eels). ** Family Muraenidae (moray eels). * Suborder ''Chlopsoidei.'' ** Family Chlopsidae (false morays). * Suborder Congroidei ** Family Congridae (congers) [incl. Macrocephenchelyidae; Colocongridae]. ** Family Derichthyidae (long-neck eels) [incl. Nessorhamphidae]. ** Family Muraenesocidae (pike congers). ** Family Nettastomatidae (duckbill eels). ** Family Ophichthidae (snake eels). * Suborder ''Moringuoidei.'' ** Family Moringuidae (spaghetti eels). * Suborder Saccopharyngoidei. ** Family Eurypharyngidae (pelican eels, umbrella-mouth gulpers). ** Family Saccopharyngidae. ** Family Monognathidae (one-jaw gulpers). ** Family Cyematidae (bobtail snipe eels). * Suborder Anguilloidei. ** Family Anguillidae (freshwater eels). ** Family Nemichthyidae (snipe eels). ** Family Serrivomeridae (saw-tooth eels). In some classifications, the family Cyematidae of bobtail snipe eels is included in the Anguilliformes, but in the Fish-Base system that family is included in the order Saccopharyngiformes. The electric eel of South America is not a true eel, but is a South American knife-fish more closely related to the carps and catfishes. Phylogeny: Phylogeny based on Johnson et al. 2012.10 |- |   |} |- |   |- |   | rowspan="2" | |- |   |} |- |   |} |- |   |} |- |   |- |   | rowspan="2" | |- |   |- |   | rowspan="2" | |- |   |} |- |   |- |Anguilloidei | rowspan="2" | |} |} |} |} |} |} |} |} |} Commercial species: